Navigation systems mounted in vehicles have the function of displaying, along with map information of its surroundings, a host vehicle position that is detected by such autonomous methods as a GPS (Global Positioning System), a gyrosystem, etc.
Further, positional accuracy becomes higher the closer the host vehicle position displayed on the navigation system is to the actual host vehicle position. By outputting highly accurate host vehicle positions, passengers are able to obtain appropriate road information with respect to the actual host vehicle position, and it is possible to improve passenger comfort.
With conventional navigation systems, the estimation accuracy for the host vehicle position was low, and it was difficult to determine the lane the host vehicle is traveling in with respect to roads having a plurality of lanes with the same direction of traffic, that is, so-called roads with a plurality of lanes in each direction. As such, in giving directions for forks in highways, or in giving directions on which way to go at intersections, differentiated route guidance per lane could not be provided, and it was difficult to improve passenger comfort. In other words, in order to achieve advanced route guidance, it is necessary to accurately determine the lane the host vehicle is traveling in.
Now, there exists a vehicle-mounted navigation device that: determines a lane change by way of a winker operation signal and of a signal from a division line detection part (division-line crossing); determines the position of the lane that the host vehicle is traveling in; detects a fork ahead; and, based on the determined lane, gives directions regarding the fork to the driver at a position that precedes by a predetermined distance (see Patent Document 1). In addition, there exists a vehicle control device that determines the lane being traveled based on the kind (solid or dashed) of the division line (see Patent Document 2). Further, there exists a vehicle positioning device that measures the host vehicle position by extracting a white line from an image, computing the travel vector of the host vehicle based on the change in distance over a given period of time, and adding the travel vector (see Patent Document 3).    Patent Document 1: JP Patent Publication (Kokai) No. 2006-23278 A    Patent Document 2: JP Patent Publication (Kokai) No. 2000-105898 A    Patent Document 3: JP Patent Publication (Kokai) No. 2007-278813 A